Signaling by frequency modulation



Aug. 3 0, 1932. BQHM 1,874,869

SIGNALING BY FREQUENCY MODULATION I Filed July 8, 1929 INVENTOR OTTO BQEHM ATT'oRriEY Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE OTTO BOHM, F BERLIN, GERMANY, ASSIGNOR TO TELEEUNKEN GESELLSCHAFT FOR DRAHTLOSE TELEGBAPHIE M. B. H., 015 IBEIRLIN,

GERMANY SIGI TALING BY FREQUENCY MODULATION Application filed July 8, 1929, Serial No. 376,606, and in Germany July 19,1928.

In operating a tube transmitter it has been suggested in the prior art to influence its frequency of oscillation instead of its amplitude at the rhythm of the voice or signal oscllla- .tions. g l

The present invention is based upon an appreciation of the basic fact that the natu ral period of a crystal is a function of the space or distance between its electrodes. The arrangement herein disclosed therefore, is based'upon the feature that a thermionic tube generator used for transmitting work has a crystal connected in the circuit governing the frequency or wave-length, said crystal being provided with one or two elastic electrodes which, by action of the voice oscillations, are caused to vibrate in a way similar to a microphone diaphragm. I

One embodiment of the idea underlying the invention is diagrammatically illustrated in the accompanying drawing.

The scheme there shown comprises two tubes, an oscillator a and an amplifier b. The wave-length of the transmitter is essentially governed by the crystal is included inthe oscillation circuit of the said oscillator, and whose upper electrode directly or indirectly is capable of oscillating for example, by action of the voice vibrations sent into the mouthpiece M.

I claim as my invention: V

In a frequency modulation system, an electron discharge device having an anode a cathode and a control electrode, a source of anode potential connected to said anode and cathode, a choke coil intermediate said source and said anode, a high frequency inductance coil connected between said control electrode and cathode, a connection from a point intermediate the ends of said high frequency inductance coil to said anode, said connection including a serially connected condenser for preventing the application of anode potential to said control electrode, a piezoelectric crystal having a pair of electrodes one' of which is movable in accordance with sound waves, connections from said electrodes to oppoiste ends ofsaid high frequency inductance coils whereby the frequency of oscillations generated by said electron discharge GERMANY, A. CORPORATION OF 7 device vary in accordance with the sound waves impinging upon said-movable piezo-, electric crystal electrode, an amplifier coupled to said high frequency inductance coil for amplifying the output of said electron discharge device, and means for radiating the output of said amplifier. j

DR. OTTO BOI-IM. 

